1. Field of the Invention
The present invention relates to a hook apparatus which is used to lift a heavy object, e.g., an iron plate, a block member, etc., at a construction site or the like.
More particularly, the present invention relates to a hook apparatus specially used for lifting a heavy object being hooked, which is designed to be capable of reliably and readily hooking and lifting such a heavy object without danger of falling and of being readily removed from the object.
2. Description of the Related Art
Hitherto, heavy iron plates (e.g., several tons) have been used at many construction sites where they are laid out on the ground to form curing scaffolding for soft ground it is frequently necessary to move such plates, depending upon the type of work at the construction site. To move the plates, a lifting operation is conducted with a crane or the like.
More specifically, the operation of lifting and moving an iron plate used as the above-described scaffolding is carried out with a wire passed through a lifting hole that is provided in a desired portion of the iron plate. The wire is engaged with a hook to pull the wire, thereby lifting and moving the iron plate.
Conventional hooks generally used for the above operation of lifting the iron plates (also known as sole plates) are of different types, such as:
(i) In one conventional hook structure, a fall preventing plate is disposed on the hook body in such a manner that the plate is biased by resilient force to abut against the distal end portion of the hook, and the width of the opening at the distal end portion of the hook is set at an extremely small value. Needless to say, the reason why the opening width at the distal end portion of the hook is made small is to prevent disengagement of the wire from the hook as much as possible;
(ii) In another conventional hook structure, a hook comprises a hook support and a hook member, which are two separate members capable of pivoting relative to each other. It should be noted that when a heavy object is lifted, the respective distal end portions of the hook support and the hook member abut against each other to function as a fall preventing mechanism.
However, this type of conventional hook structure is also used in such a way that a wire attached to an iron plate is engaged with the hook member; therefore, the width of the opening which is defined at the hook distal end portion between the hook support and the hook member when pivoted relative to each other is extremely small for the same reason as above.
In field work, however, heavy labor is required for the operation of engaging a wire with an iron plate laid out, which is as heavy as several tons. Therefore, the worker is apt to insert the engagement portion of the hook (i.e., the hook distal end portion) directly into a hole provided in the iron plate to lift it. In such a case, however, it is extremely difficult to engage the hook with the iron plate because the opening width at the hook distal end portion is extremely small, as described above. In other words, when an object, e.g., an iron plate, which has been laid out on the ground is to be lifted up by engaging the hook directly with the iron plate, the hook cannot readily be engaged with the iron plate because the opening width of the conventional hook is extremely small. Even if the hook is successfully engaged with the iron plate, it is still difficult to disengage the hook from the iron plate after the iron plate has been relocated.
Properly speaking, hooks having no fall preventing device must not be used for the operation of the type described above, but in many work sites hooks which are equipped with no fall preventing device and which have a large opening width are used in the present state of art.
However, it is considerably dangerous to use a hook which is equipped with no fall preventing device and which has a wide opening for such an operation.
More specifically, when an iron plate (as a heavy object) is being lifted with a hook having no fall preventing device, there is substantially no possibility of the hook disengaging from the iron plate, but when the iron plate is lowered onto the ground so as to be installed thereon, a play is likely to be produced between the hook and the hole for lifting due to slacking of the lifting wire. Thus, undesired disengagement of the hook from the hole frequently occurs. Once the hook disengages from the hole, the iron plate will fall down, inviting danger of people being crushed to death under the iron plate. In actuality, there have been many fatal accidents caused by falling iron plates at work sites of the kind described above.
The present inventor conducted exhaustive studies in order to solve the above-described problems of the prior art.
As a result, the present inventor has found that if a hook apparatus has such a structure that a hook that is pivotably attached to a hook support is capable of pivoting approximately 180.degree. reversely from a locked position (in which the distal end portion of the hook is held in united relation to a fall preventing portion of the hook support to maintain a locked state) when it is unlocked, that is, if the distal end portion of the hook and the fall preventing portion of the hook support can be opened relative to each other much wider than in the prior art, it is possible to facilitate insertion of the distal end portion of the hook into an engagement hole provided in a heavy object, e.g., an iron plate or the like laid out on the ground, when the hook is to be engaged with such a heavy object to lift it, and there is no likelihood that the fall preventing portion will abut on or be buried in the ground during the operation of disengaging the hook from the heavy object, thus enabling the hook to be disengaged from the heavy object extremely smoothly without meeting with any obstacle. On the basis of this finding, the present inventor has previously proposed a hook apparatus with a novel structure (see Japanese Patent Application No. 3-216524).
Particularly, the hook apparatus for lifting a sole plate, which has previously been proposed by the present inventor, exhibits advantageous effects in the process of hooking and lifting a sole plate which has been laid out with the hook and moving it to a predetermined place. That is, the proposed hook apparatus has great advantages in that the hook can be readily and reliably engaged with a hole for lifting provided in the sole plate, and that it is possible to surely prevent the fall of the plate during conveyance, and further that there is no likelihood of the hook disengaging from the sole plate even if the lifting rope slacks when the plate being hooked is lowered to the place where it is to be laid out.
However, the proposed hook apparatus still has some difficulties in removing the hook apparatus from the sole plate after it has been conveyed and laid out in a predetermined place.
As has been described above, the proposed hook apparatus has no likelihood that the fall preventing portion of the hook support will abut on or be buried in the ground or other object when the sole plate being hooked is lowered to where it is to be laid out. Therefore, the fall preventing portion does not interfere with the subsequent operation of disengaging the hook from the plate. However, since the disengaging operation depends on the worker, it is not easy to remove the whole hook apparatus from the sole plate, which is as heavy as several tons, apart from the advantage in terms of the structure of the fall preventing portion.
Under the above-described circumstances, it is an object of the present invention to provide an improvement of the hook apparatus previously proposed by the present inventor, particularly a hook apparatus having a mechanism for facilitating the removal of the hook apparatus from a sole plate or other heavy object.